1. Field of the Invention
The invention relates generally to boat hulls. More particularly, the invention relates to a boat hull for an air thrust propeller driven boat. The invention further relates to a boat hull for an air thrust propeller driven boat which upon reaching high speeds hydroplanes over the surface of the water.
2. Description of the Related Art
Air thrust propeller driven boats, or "air boats" as they are commonly known, have found wide range application and acceptance in areas where shallow water, reeds, everglades and subsurface debris present hazards to the operation of a submersed propeller. A significant advantage associated with air boats is their ability to hydroplane over the water's surface, and therefore, they require no significant water depth for effective operation.
An air boat operates generally on the principle that once high speeds are reached, the hull of the boat hydroplanes over the surface of the water, having relatively little impact on whatever lies beneath the surface of the water. Reaching the speeds necessary for hydroplaning, or "getting up on the plane", as it is generally termed in the vernacular, requires a significant amount of power depending upon the size of the boat.
Once an air boat reaches an appropriate speed, it will hydroplane. Once a boat begins to hydroplane, there is friction between the water surface and the bottom of the boat hull. Friction absorbs energy, thus reducing the speed and efficiency of the boat.
A number of boat hull designs have attempted to reduce the energy loss due to friction between the water surface and the bottom of a boat hull. One such attempt is disclosed in U.S. Pat. No. 2,842,084 to Williams wherein a boat hull is equipped with a series of channels open to the water surface. Air pumped into the channels lifts the boat, thus reducing water friction. A disadvantage of this design is that the bottom of the boat is not flat but rather has a series of projections forming the air filled channels. These projections are not desirable in air boat design.
In British patent application No. 996,477 filed Feb. 8, 1962 discloses an air thrust propeller driven boat having a second propeller. The second propeller produces a flow of air through a plenum chamber which extends through the mid-portion of the hull and discharges air beneath the boat, thus lifting the boat from the water surface. A disadvantage of this design is that a major portion of the boat loses utility due to the extreme size of the second propeller. Surface area is lost from the upper deck in order to incorporate the second propeller into the design of the boat. Further, this design makes direct use of the engine power and does not appear to enhance the efficiency of the engine which powers the propeller.
Typically, air boats are powered by an aircraft engine mounted high above the water line of the boat hull to provide adequate clearance for the rotating propeller. Aircraft engines used in air boats are generally expensive, heavy, extremely powerful, noisy and generally have poor fuel economy.
The use of a water-cooled engine in marine applications has a number of advantages over the use of an air-cooled engine. For example, a water-cooled engine is not as noisy as an air-cooled aircraft engine and generally has better fuel economy. However, a disadvantage associated with the use of water-cooled engines in marine applications, is that water-cooled engines require a circulating water cooling system. Typically, a circulating water cooling system in a boat draws water through an opening in the hull of the boat, circulates the water through the engine and expels it either out of the exhaust or out a rear portion of the hull. A cooling system such as this is generally called an "open loop" system.
Another type of cooling system called a "closed loop" circulating water cooling system, has a heat exchanging radiator for dissipating heat from the engine. Water circulated through the engine absorbs heat. The water is pumped to the radiator where the heat dissipates into the environment. The water then return to the engine and the cycle or "loop" repeats itself.
In boats where the engine is covered by a cowl or engine cover, marine codes require that exhaust manifolds on the engine be water cooled. Typically, exhaust manifolds in power boats are cooled by an "open loop" cooling system. However in an air boat, where the boat hydroplanes over the surface of the water, an "open loop" system is not practical, since there is no easy way to draw water into the system. Unfortunately, if a "closed loop" cooling system is used to cool both the exhaust manifolds of the engine and the engine itself, an extremely large radiator will be necessary in order to dissipate all the heat produced by both. Therefore, a single "closed loop" system used to cool both the exhaust manifolds and the engine is impractical.